1. Technical Field
The present invention relates in general to thermal control for electronic systems and, in particular, to thermal control for electronic systems including modular processor-based components.
2. Description of the Related Art
A modular computing system, such as a rack-mounted server, may include a modular enclosure or housing for a variety of computing components. This modular enclosure typically contains an integrated power supply, cooling system, communication connections and data storage. The modular enclosure allows the use of simplified components that may be smaller and potentially cheaper than standard components.
A modular computing system may include a variety of processor-based computing components, selected by a user and connected via the modular enclosure. The modular enclosure provides a physical structure to support and connect computing components within a compact space. The number of components and their spatial arrangement within the housing may be varied to suit a particular user's specific computing needs. The modular enclosure may be designed to allow a user to plug in, for example, hundreds of computer components at one time. The components can be plugged into a modular housing in a wide variety of user-selected configurations.
As will be appreciated, modular computing system will include numerous electrical components, such as processors or central processing units (CPUs), which draw electrical current to perform their intended functions. Any electrical device through which electrical current flows produces heat. The amount of heat any one device generates generally is a function of the amount of current flowing through the device. Consequently, placing numerous computing components in close proximity within a modular enclosure generally creates thermal issues and necessitates the use of a cooling system within the modular enclosure.
Typically, each integrated circuit manufacturer designs its products to operate correctly within a predetermined temperature range. If the temperature exceeds the predetermined range (i.e., the device becomes too hot), the integrated circuit device may not function correctly, thereby potentially degrading the overall performance of the computer system. Thus, it is desirable for a computer system generally and its components specifically to operate within a thermally benign environment.
Some computers implement two techniques for cooling the computer's internal electrical components. One technique, called “passive” cooling, slows down the operating speed of a component so that the component will produce less heat. For example, the clock frequency of a CPU operating at 2 GHz may be reduced to lower frequency, such as 1.5 GHz. With fewer transistor state changes occurring per second, less current flows through the CPU each second, and thus, less heat is generated by the device.
The second cooling technique, referred to as “active” cooling, uses one or more fans to force air around one or more “hot” components through a vent and outside the computer. Thus, active cooling removes the warm air from a computer. A typical modular enclosure may cool its internal components utilizing fans at the rear of the housing, which pull air through the interstices between components and out the back of the modular enclosure.
Forced air cooling may become less effective when the slots in a modular enclosure are not fully populated. A slot without a component installed offers no resistance to the airflow, causing a greater proportion of the airflow to move through the empty slot and significantly less airflow to move through the interstices between other components. The result is a reduced cooling effect, potentially causing the installed components to overheat. An airflow restrictor may be installed in an empty slot to block airflow; however, in some cases the airflow restrictor may only somewhat restrict airflow, thus reducing but not eliminating the potential for overheating caused by airflow reduction. Flaps may also be attached to the openings to hang over the space and can be used in some cases to provide a filler-like restriction of the airflow through unused and empty slots.
Overheating conditions are typically monitored using temperature sensors. A cooling system may be programmed to respond to an overheating condition by changing fan speeds, changing a clock frequency for one or more components, or otherwise altering the thermal environment. These reactive responses to an overheat condition may result in damage to the hardware despite the response because the damage caused by overheating may be immediate.